Typically headers for combine harvesters are mounted on the feeder house of the combine with the mounting arrangement providing a floating action of the header relative to the feeder house so that the cutter bar can rest on the ground and float over the ground in a cutting action.
In some cases an automatic header height control system is provided with header to feeder house position indicators which allow the header to automatically adjust flotation to ground conditions, eliminating the need for the operator to make constant adjustments.
In some cases however it is desirable to provide a cutting action at a position where the cutter bar is at a raised height so that no stability is provided by engagement with the ground. In this arrangement, the header is typically provided with ground engaging gauge wheels at or adjacent respective ends of the header to gauge a required height from the ground.
This is normally done with gauge wheels that carry part of the weight of the header, with the rest carried by the main suspension, with springs on the gauge wheels in order to absorb the high shock loads when hitting a bumps and in order to provide some adjustment of cutter bar height while maintaining wheel engagement with the ground.
One of the issues with this system is to provide sufficient stability of the header when cutting at the raised height and while traveling at higher cutting speeds.
Some of the different ways to do this and their problems include:
Gauge wheel with a soft spring, however this does not provide enough header stability;
Gauge wheel with a stiff spring, this provides more stability but the stiff spring action can “throw” the header up to an unacceptable degree;
Gauge wheel with a stiff spring as above but combined with a shock absorber, this is better than the spring alone as above, but there remain issues with stability;
Gauge wheel mounted solid on the header, this does not allow changing the height of the cutter bad while maintaining ground contact with the gauge wheel s and causes huge shock loads;
Ground sensors in place of the gauge wheels to provide direct control signals to the suspension system, but this system does not react quickly enough to provide the required control and stability. Also, with ground sensors the header has to be positioned on a bottom stop when cutting off the ground so that the header is effectively fixed relative to the combine. As a result, when the combine goes over bumps the oscillation of the combine causes the header to move up and down, causing an irregular cut.